Our Milky Way has more than 100 million black holes

There may be as many as 100 million black holes in the Milky Way galaxy, according to scientists, including one of Indian origin, who conducted a cosmic survey to calculate and categorise the enigmatic, dark objects. The celestial census began more than a year and a half ago, shortly after the news that the Laser Interferometer Gravitational-Wave Observatory (LIGO) had detected ripples in the space-time continuum created by the distant collision of two black holes, each the size of 30 suns.

“Fundamentally, the detection of gravitational waves was a huge deal, as it was a confirmation of a key prediction of Einstein’s general theory of relativity,” said James Bullock, University of California, Irvine (UCI) in the US.

“But then we looked closer at the astrophysics of the actual result, a merger of two 30-solar-mass black holes. That was simply astounding and had us asking, ‘How common are black holes of this size, and how often do they merge?’” Bullock said.

Scientists assume most stellar-remnant black holes – which result from the collapse of massive stars at the end of their lives – will be about the same mass as our Sun. To see the evidence of two black holes of such epic proportions coming together in a cataclysmic collision left some astronomers puzzled.

The new research was an attempt to interpret the gravitational wave detections through the lens of what is known about galaxy formation and to form a framework for understanding future occurrences.

According to Manoj Kaplinghat, professor at UCI, the number of black holes of a given mass per galaxy will depend on the size of the galaxy.